1. Field of the Invention
The present invention relates to a fuel supply apparatus for an internal combustion engine, and more particularly to a fuel supply apparatus for an internal combustion engine including a first fuel injection mechanism for injecting fuel into a cylinder (in-cylinder injector) and a second fuel injection mechanism for injecting fuel towards an intake manifold and/or an intake port (intake manifold injector).
2. Description of the Background Art
There is known a fuel supply apparatus (fuel injection apparatus) including an intake manifold injector for injecting fuel into an intake port and an in-cylinder injector for injecting fuel into a cylinder to inject fuel by a combination of intake manifold injection and in-cylinder direct injection by controlling the intake manifold injector and in-cylinder injector in accordance with the driving state.
Such a fuel supply apparatus must have the fuel injection pressure from the in-cylinder injector increased in order to directly inject fuel into a cylinder. To this end, there is disclosed a configuration of discharging fuel from a fuel pump through a low pressure fuel pump common to a high pressure fuel supply system for in-cylinder injection and a low pressure fuel supply system for intake manifold injection, wherein the fuel from the low pressure fuel pump is further boosted by a high pressure fuel pump at the high pressure fuel supply system to be supplied to the in-cylinder injector (for example, Japanese Patent Laying-Open No. 2001-336439; referred to as Patent Document 1 hereinafter).
Patent Document 1 discloses the technique of appropriately setting the fuel injection ratio between the fuel injection quantity towards the cylinder and the fuel injection quantity into the intake manifold, taking into account atomization of the injected fuel in the cylinder in an internal combustion engine including the fuel supply apparatus set forth above.
In the internal combustion engine, the fuel injection ratio between the in-cylinder injector and intake manifold injector changes according to the state of the internal combustion engine. In order to inject fuel properly from the in-cylinder injector according to such a fuel injection ratio, the configuration of controlling the fuel pressure at the target pressure is important in the high pressure fuel supply system. If the fuel pressure is not controlled at the target pressure, burning will be degraded due to change in the atomization state and/or the fuel injection quantity, leading to the possibility of unstable output from the internal combustion engine.
Particularly in the internal combustion engine set forth above, an in-cylinder injection suppressing period during which fuel injection from the in-cylinder injector is suppressed will occur according to the setting of the fuel injection ratio. The controllability of the fuel pressure at the time of the in-cylinder injection suppressing period and at the time of resuming in-cylinder injection will become an issue in order to conduct fuel injection properly at the time of resuming fuel injection from the in-cylinder injector subsequent to the in-cylinder injection suppressing period.